Rotating compressors are well known which increase the temperature and the pressure of a gas. Common are centrifugal compressors which often include several stages of compression interconnected through conduits and intercoolers which cool the compressed gas between the plural stages. A typical compression stage includes a so-called scroll which houses an impeller. The impeller is mounted on a shaft or pinion which enters the scroll through a seal. An inlet piece is rigidly mounted to the scroll so that the impeller is positioned closely adjacent to the inlet piece and the scroll. For best efficiency, the clearances between the impeller and the scroll, and the impeller and the inlet piece, are closely maintained. During operation these clearances may be, for example, in the range of thirty thousandths of an inch. Relative motion or contact among the impeller and the scroll or the inlet piece could cause damage to the compressor and can significantly affect its efficient operation.
During operation a compressor experiences many forces as a result of temperature and pressure changes. The impeller is rotating at high rotational velocity and is affixed to the pinion which engages a gear supported in a gear box. The gear box and the components therein can expand and contract at a given rate. The scroll is typically affixed to the gear box. The scroll itself, although typically manufactured of high strength steels, tends to blow up, in an exaggerated sense somewhat like a balloon. The inlet piece is connected to inlet piping which transmits forces. The volute or discharge of the scroll is connected directly, or through interstage components, to discharge piping or intercoolers which also expand and contract under operating conditions.
It is important, therefore, to accommodate the various forces and motions while closely maintaining the clearances about the impeller.
In the prior art the scroll and downstream components have been interconnected and mounted in many ways. A common interconnection between a scroll and an intercooler involves fabricating the intercooler and the scroll with flanges and using a flanged spool piece rigidly affixed between the intercooler and spool through bolted flanged connections. This rigid assembly directly transmits loads between the intercooler and scroll. Consequently, to accommodate thermal expansions such designs have often used complex configurations to mount the intercooler in a spring like fashion from, for example, the gear box or compressor base. A concern with such designs is that the intercooler is also interconnected to other components and movement of the intercooler undesirably transmits forces to the other components. Such designs do not directly address certain forces associated with operating pressures.
An improvement upon the rigid flanged systems is the use of a nonflanged spool piece or conduit interconnected between the scroll and intercooler through peripheral grooved pipe couplings. Each end of the spool piece in such designs is spaced from the respective scroll and intercooler to form a space which will allow thermal growth between the components tending to close the space as the compressor heats up. The peripheral pipe coupling, including a coupling housing and a gasket, seals about the exterior of the components across the space, and allows movement of the components toward one another. Such peripheral grooved pipe couplings are commercially available from the Victaulic Company of America, Easton, Pa.
While the nonflanged design is an improvement in that it accommodates axial growth due to thermal forces tending to move the scroll and downstream components toward one another, it does not directly alleviate pressure forces imposed on the scroll and the downstream component, such as an intercooler. The pressure forces tend to move the scroll and the intercooler away from one another. Because of the shape and mounting of the scroll, the angles among the various components, the pressure forces, thermal forces, and resulting moments, a tendency for movement of the scroll can occur in almost any direction, undesirably changing the clearance between the scroll, the inlet piece and the impeller. It is desirable to provide structure which better accommodates pressure as well as thermal forces among centrifugal compressor components, particularly to closely maintain clearances about the impeller during operation.